Compared with women, much less is known about the etiology and prevention of osteoporosis and osteoporotic fractures in older men. Despite the substantial progress in osteoporosis-related research, the pathophysiology of osteoporosis remains incompletely understood. Recent studies have suggested a novel factor, bone marrow fat (BMF), as a potential cause or consequence of age-related osteoporosis due to the observation of higher BMF in osteoporotic subjects and its underlying relationship with osteoblast and adipocyte genesis. Broader study of the relationships between BMF and skeletal health has become feasible recently with the availability of non-invasive techniques for assessing bone marrow. To our knowledge, only a handful of studies have directly examined the connection between BMF and bone mineral density (BMD), and these studies have largely focused on Chinese men and women. Many aspects of the role of BMF on osteoporosis remain largely unknown. First, it is not clear whether the inverse association between BMF and areal BMD observed in the Chinese population can also be generalized to US populations. In addition, the conventional areal BMD assessment only provides partial information on bone strength. Whether or not BMF is associated with true volumetric BMD, bone strength, and bone formation/resorption regulation requires further investigation. The current application seeks to improve our understanding of the connection of BMF with bone density, geometry and turnover by recruiting 150 men who are currently participating in the Osteoporotic Fractures in Men (MrOS) study at the Pittsburgh clinic site. Vertebral BMF will be quantified using the-state-of-the-art Magnetic Resonance Spectroscopy technique. Dual energy x-ray absorptiometry (DXA) and peripheral quantitative tomography (pQCT) will be employed to obtain measures of bone density (areal and volumetric), size and strength. In addition, bone turnover markers and a database of lifestyle, medical and anthropometric characteristics will also be available to evaluate the link between BMF and skeletal health. This proposed study will provide the research community with novel understanding toward the etiology of osteoporosis, especially in older men. It also opens a new opportunity for prevention and/or treatment of osteoporosis and osteoporotic fractures among at-risk populations.